Re: [PATCH] rust: upgrade to Rust 1.75.0

[Martin Rodriguez Reboredo <yakoyoku@gmail.com>]

On 12/24/23 14:21, Miguel Ojeda wrote:
> This is the next upgrade to the Rust toolchain, from 1.74.1 to 1.75.0
> (i.e. the latest) [1].
> 
> See the upgrade policy [2] and the comments on the first upgrade in
> commit 3ed03f4da06e ("rust: upgrade to Rust 1.68.2").
> 
> # Unstable features
> 
> The `const_maybe_uninit_zeroed` unstable feature [3] was stabilized in
> Rust 1.75.0, which we were using in the PHYLIB abstractions.
> 
> The only unstable features allowed to be used outside the `kernel` crate
> are still `new_uninit,offset_of`, though other code to be upstreamed
> may increase the list.
> 
> Please see [4] for details.
> 
> # Other improvements
> 
> Rust 1.75.0 stabilized `pointer_byte_offsets` [5] which we could
> potentially use as an alternative for `ptr_metadata` in the future.
> 
> # Required changes
> 
> For this upgrade, no changes were required (i.e. on our side).
> 
> # `alloc` upgrade and reviewing
> 
> The vast majority of changes are due to our `alloc` fork being upgraded
> at once.
> 
> There are two kinds of changes to be aware of: the ones coming from
> upstream, which we should follow as closely as possible, and the updates
> needed in our added fallible APIs to keep them matching the newer
> infallible APIs coming from upstream.
> 
> Instead of taking a look at the diff of this patch, an alternative
> approach is reviewing a diff of the changes between upstream `alloc` and
> the kernel's. This allows to easily inspect the kernel additions only,
> especially to check if the fallible methods we already have still match
> the infallible ones in the new version coming from upstream.
> 
> Another approach is reviewing the changes introduced in the additions in
> the kernel fork between the two versions. This is useful to spot
> potentially unintended changes to our additions.
> 
> To apply these approaches, one may follow steps similar to the following
> to generate a pair of patches that show the differences between upstream
> Rust and the kernel (for the subset of `alloc` we use) before and after
> applying this patch:
> 
>      # Get the difference with respect to the old version.
>      git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
>      git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
>          cut -d/ -f3- |
>          grep -Fv README.md |
>          xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
>      git -C linux diff --patch-with-stat --summary -R > old.patch
>      git -C linux restore rust/alloc
> 
>      # Apply this patch.
>      git -C linux am rust-upgrade.patch
> 
>      # Get the difference with respect to the new version.
>      git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
>      git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
>          cut -d/ -f3- |
>          grep -Fv README.md |
>          xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
>      git -C linux diff --patch-with-stat --summary -R > new.patch
>      git -C linux restore rust/alloc
> 
> Now one may check the `new.patch` to take a look at the additions (first
> approach) or at the difference between those two patches (second
> approach). For the latter, a side-by-side tool is recommended.
> 
> Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1750-2023-12-28 [1]
> Link: https://rust-for-linux.com/rust-version-policy [2]
> Link: https://github.com/rust-lang/rust/issues/91850 [3]
> Link: https://github.com/Rust-for-Linux/linux/issues/2 [4]
> Link: https://github.com/rust-lang/rust/issues/96283 [5]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> [...]

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>